The invention relates to a denture set of prefabricated teeth, which has at least one first tooth, selected from a group of teeth intended for one jaw, and at least a second tooth selected from a group of antagonists intended for the other jaw, and the teeth have at least one contact point, on the surfaces disposed facing the antagonists, with which contact point the antagonist comes into contact.
Until now, in the production of dentures, the procedure was that first, from a prefabricated set of artificial teeth, the dental technician set up the individual teeth in an articulator on a wax model taken from the jaw of the patient. In this setting up process, he orients himself in accordance with certain principles. For instance, the edge of the side teeth, that is, the apexes of the tooth cusps, should be located on a line that corresponds to Spee""s curve. The buccolingual cusp tangents should be inclined slightly, and increasingly from the second premolar to the second molar, toward the floor of the mouth. This is in accordance with Wilson""s theory, according to which the tooth cusps should be located on a transversally extending curve. In the setup of the teeth, a cutout of a spherical dome can therefore be used, against which the teeth each come to rest with their upper edge. This procedure is in accordance with Monson""s theory. After the setup of the teeth in wax, a trial of the wax model in the patient, and subsequent polymerization, the prosthesis is ground in an articulator, in order to adapt the engagement of the teeth of the upper and lower jaws. The goal here is to allow only point-type contacts rather than any contact surfaces. Another need is that the denture balance on both sides; that is, in the closed position with complete intercuspidation, the molars of the upper and lower jaws should mesh with one another on both sides and form contact points. This bilateral balancing, which is not in accordance with natural conditions, is intended to prevent the denture from being pried out and thus tilting out of the way in the intercuspidation position. This adaptation is done by having the dental technician, after he has set up the teeth, machine the chewing surfaces of the teeth by grinding them down until such time as the teeth of both halves of the jaw are balanced and the desired number of contact points has been achieved. Once this is finished, the denture is placed in the mouth of the patient and further machined by the dentist, until the patient has the subjective feeling of an acceptable adaptation of the denture.
In known false teeth, or dentures, the precise location of the contact points between the teeth of the upper and lower jaws is accordingly accomplished only during machining. Because of the machining during the adaptation, the vertical height is also reduced. The term xe2x80x9cvertical heightxe2x80x9d is understood to mean the relative position of the upper and lower jaws, or in the final analysis the distance between the jaws, measured vertically. This distance is reduced, however, by the grinding down of the teeth during the adaptation of the denture. Thus during the construction and adaptation, the shape of the denture becomes farther and farther away from the natural conditions that are predetermined by the jaw itself. As a result, the location of the jaws relative to one another and thus the location of the condyles in the joint are determined by the positioning of the artificial teeth in the denture. This is contrast to natural conditions, in which the location of the condyles in the joint and the shape of the jaw in the final analysis determine the location of the teeth, because the teeth change their position until such time as they have adapted to the conditions predetermined by the jaws and the mandibular joint.
As a consequence, a number of problems arise in the dentures made with known artificial teeth, and these problems are a severe burden to the patient.
Since the position of the condyles in the joint is determined by the arrangement of the artificial teeth, the result, unless this position matches the natural one, is muscle stresses and pains, since the jaw is forced into an unnatural position in the closing position. To overcome this, the dentist grinds off further contact points. This further reduces the vertical height and hence under some circumstances shifts the condyles even farther out of their natural position. As a result, the patient can never have well-seated dentures; finally, the only remaining option is to remake the denture, yet once again the same difficulties stand in the way of a good denture fit.
Rapid denture wear is also caused by the shifting of the condyles out of their natural position that occurs in the intercuspidation position. During the process of closing of the jaw, while the tooth cusps are outside the closing position they meet the antagonist and then slide along its surface to reach the closing position. After being worn for only a short time, worn surfaces develop in the denture, leading to the formation of still more contact points or contact surfaces.
Since the final disposition of the contact points does not result until during the machining, it is moreover not assured that the forces initiated into the tooth will add up to a resultant in the direction of the tooth center line. Heavy loads in the tooth that have a horizontal force component can thus occur, which once again leads to premature wear of the denture.
A further disadvantage of this random arrangement of contact points is that in the closing motion, not all the contact points develop simultaneously. An excess number of contact points can also occur. As a result, the patient loses his feel for the closing position in the biting process, which is perceived as extremely irritating. Finally, contact points can also come to rest on oblique surfaces. There is then the risk in the closing motion that the antagonist will slip off, resulting in high peak loads on the tooth.
Previously known artificial teeth for a dental prosthesis or denture take the biomechanical conditions, which are predetermined by the motions of the jaw, into account only inadequately, if at all. For instance, the design of the denture set disclosed in German Patent DE 195 087 62 C2 is directed solely to the contacts between opposing teeth in a static state of maximal intercuspidation. The relationships of the tooth surfaces during the natural motions of the jaw remain unaddressed.
The object of the invention is therefore to furnish a denture made of artificial teeth in which better adaptation of the denture to the anatomical conditions of the patient, which are determined by the position of the condyles in the mandibular joint and by their path of motion.
In a denture set of the generic type in question, this object is attained by the bodies of claims 1 and/or 9 and/or 10 and/or 13.
In particular because at least three contact points (5) are provided in each fossa of a respective molar or premolar, with which contact points a chewing cusp of the antagonist comes into contact in the intercuspidation position, a substantially better prosthesis is obtained. The molars develop a plurality of contact points, while only one or two contact points are developed between the canines and incisors.
If at least five contact points per molar or premolar are provided, then each premolar or molar, with its chewing cusp, forms a common contact point with the chewing cusp of the antagonist.
Since until now the upper edge of the artificial teeth was disposed on the compensation curves, the location of the contact points was indeterminate. In the denture set of the invention, the location of the contact points is predetermined in that the contact points are disposed on a sagittal compensation curve and transversal compensation curve that are determined by the motion of the condyles of the mandible. The positioning of the artificial teeth is therefore determined by the location and the curvature of the compensation curves and thus by the anatomical conditions of the jaw and the mandibular joint. Shifting of the tooth along the mandibular arch in the distal or mesial direction is possible, with the contact points always located on the compensation curves. Upon shifting, there is accordingly no need to tolerate any loss of vertical height, either. The compensation curves can correspond to the curves of von Spee (sagittal) and Wilson (transversal), or the spherical curve of Monson, which forms a cutout from a spherical surface. As a result of the curvature of the compensation curve, the slope of the articulation path can be compensated for, and it is thus possible to adapt the denture to the angle of inclination of the cusps. The arrangement of contact points within one tooth should be as close as possible to a plane that is defined by the compensation curves of von Spee and Wilson or Monson. However, it should be taken into account that these curves are merely model concepts. It has been demonstrated, however, that slight deviations from the desired ideal state, which are due to individual anatomical differences among various patients on the one hand and to the need for a standardized tooth on the other, are compensated for by the relationships of the paired antagonists. Deviations on the order of magnitude of 5% of the tooth diameter are typical.
Since all the contact points are located at the same height, it proves to be a further advantage that in an opening motion, all the contacts between the molars of the upper and lower jaws are undone simultaneously, or in a closing motion are formed simultaneously. Especially in the latter type of motion, the result is a uniform force distribution on all the teeth; that is, peak forces, which are unavoidable if contact forms prematurely between individual teeth, do not occur.
Centering of the chewing cusp of the antagonist in the fossa of the artificial tooth is done by providing three contact points in the fossa of the tooth, at which contact points, in the intercuspidation position, a chewing cusp of the antagonist comes to rest. The contact points form a triangle, whose surface is disposed virtually perpendicular to the tooth center line. A slight inclination of the triangular surface is due to the location of the contact points on the compensation curves, which approximately form a cutout from a sphere.
The apex of the chewing cusp can slide harmonically into the intended stop position, if the contact points provided in the fossa are disposed on a spherical surface. Because of the spherical surface, there is no need for the apex of the chewing cusp to move along an exactly predetermined path into the closing position. Minor deviations from the intended path are tolerable, and the apex of the chewing cusp is directed into the closing position by sliding with its lateral surfaces along the spherical surfaces.
The apex of the chewing cusp is prevented from slipping off if in the fossa, tripodal ridges and/or marginal ridges are provided, and the contact points are disposed on the inclines of the tripodal ridges and/or marginal ridges.
A harmonic opening motion is made possible if adjacent to the tripodal ridges and originating at the contact points, concavities are provided in the direction of the laterotrusion and/or protrusion and/or lateroprotrusion and/or mediotrusion and/or surtrusive retrusion motion of the lower jaw. The apex of the chewing cusp can then move away from the stop position, in all the natural directions of motion of the jaw, without colliding with obstacles formed by shearing cusps or a marginal ridge.
Good chewing action is brought about if that the ratio of the surface area, formed by the circumference of the tooth in plan view, to the inside surface area of the occlusal table is 55-65%.
The positioning of the artificial tooth in the vertical direction is made easier in that a marginal ridge contact is provided on the mesial and/or distal marginal ridge of the tooth. The marginal ridge contact is located at the highest point of the marginal ridges. When the teeth are set up, the marginal ridge contacts of adjacent teeth can be aligned at the same height, and a result, because of their three-dimensional relationship to the marking, all the contact points necessarily come to rest on the compensation curves. Aligning the teeth by means of the apexes of the cusps is thus omitted.
Setting up the artificial teeth in the denture set is further facilitated in that the distal surface of the tooth is embodied as a shaped surface, preferably as a convex surface, and the mesial surface of the adjacent tooth is embodied as a fitting surface, preferably a concave surface. Because of the design of the contacting surfaces of adjacent teeth, the teeth necessarily enter the correct position relative to one another.
The correct setup of the artificial teeth is further facilitated in that the teeth, viewed from the buccal or labial direction, have a tooth center line that is disposed perpendicular to the occlusion line.
By a combination of marking, the design of the adjacent surfaces of adjacent teeth, and the orientation of the tooth center line, the necessary information for disposing the contact points in a certain plane can therefore be built into the artificial tooth. In setting up the teeth, the dental technician is thus provided with aid in the form of the shape of the teeth, so that correct positioning of the teeth can be achieved easily.
The denture set of the invention can be used both for a front- or canine-tooth-guided occlusion and for a both unilateral and a bilaterally balanced occlusion, if on the working side the molars of the upper jaw have guide faces on the buccal inclines that interact with the guide faces provided on the buccal outer surface of the molars of the lower jaw, and guide faces that interact with the guide faces provided on the palatal inclines of the molars of the upper jaw are disposed on the balance side of the buccal inclines of the molars of the lower jaw. For a balanced occlusion, the canine tooth is correspondingly ground down or tilted outward. Upon a lateral motion of the lower, all the molars then always have contact with their antagonists. This prevents the denture from being tilted away by unilateral loads.
In the case of canine-tooth guidance, an unhindered opening motion is made possible if the first premolar of the upper jaw has a buccal-mesial concavity, disposed between the tripodal bead and the marginal bead, that interacts with a guide face provided distal-palatally on the canine of the lower jaw.
Front-tooth guidance is made possible if the upper incisor lingually has a guide face extending in the incisal direction from the contact point. In the opening motion, the contact point on the cutting edge of the incisor of the lower jaw can then slide along the guide face.
An adaptation in the position of the lower incisors to the inclination of the condyle path is made possible in that the lower incisor has a surface, labially adjoining the cutting edge, that is inclined by an angle of 20xc2x0-45xc2x0 to the approximal tooth center line. The surface can be oriented parallel to the condyle path, thus assuring harmonic guidance in the opening motion by the lingual guide faces.
A further adaptation of the denture is possible if the upper incisor has a surface, palatally adjoining the cutting edge, that is inclined at an angle of 20xc2x0-45xc2x0 to the approximal tooth center line.
The invention will be described in terms of a preferred embodiment in conjunction with a drawing, and further advantageous details can be learned from the drawing figures. Functionally identical elements are provided with the same reference numerals throughout.